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. 2022 Aug 9;34(15):7029-7041.
doi: 10.1021/acs.chemmater.2c01481. Epub 2022 Jul 25.

Influence of the Synthesis and Crystallization Processes on the Cation Distribution in a Series of Multivariate Rare-Earth Metal-Organic Frameworks and Their Magnetic Characterization

Raluca Loredana Vasile  1 , Agustín Alejandro Godoy  2 , Inés Puente Orench  3   4 , Norbert M Nemes  5 , Víctor A de la Peña O'Shea  6 , Enrique Gutiérrez-Puebla  1 , Jose Luis Martínez  1 , M Ángeles Monge  1 , Felipe Gándara  1
Affiliations

Influence of the Synthesis and Crystallization Processes on the Cation Distribution in a Series of Multivariate Rare-Earth Metal-Organic Frameworks and Their Magnetic Characterization

Raluca Loredana Vasile et al. Chem Mater. .

Abstract

The incorporation of multiple metal atoms in multivariate metal-organic frameworks is typically carried out through a one-pot synthesis procedure that involves the simultaneous reaction of the selected elements with the organic linkers. In order to attain control over the distribution of the elements and to be able to produce materials with controllable metal combinations, it is required to understand the synthetic and crystallization processes. In this work, we have completed a study with the RPF-4 MOF family, which is made of various rare-earth elements, to investigate and determine how the different initial combinations of metal cations result in different atomic distributions in the obtained materials. Thus, we have found that for equimolar combinations involving lanthanum and another rare-earth element, such as ytterbium, gadolinium, or dysprosium, a compositional segregation takes place in the products, resulting in crystals with different compositions. On the contrary, binary combinations of ytterbium, gadolinium, erbium, and dysprosium result in homogeneous distributions. This dissimilar behavior is ascribed to differences in the crystallization pathways through which the MOF is formed. Along with the synthetic and crystallization study and considering the structural features of this MOF family, we also disclose here a comprehensive characterization of the magnetic properties of the compounds and the heat capacity behavior under different external magnetic fields.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Combination of different metal cations results in multi-metal MTV MOFs as well as in the competitive formation of crystals with different metal combinations.
Figure 2
Figure 2
Crystal structure of RPF-4 consists of rod-shaped SBUs made of rare-earth cations connected by the organic linker H2hfipbb.
Scheme 1
Scheme 1. Depending on the Element of Choice, the Combination of Different Metal Cations in the RPF-4 Family Results in Multi-Metal MTV MOFs as Well as in the Competitive Formation of Crystals with Different Metal Combinations
Figure 3
Figure 3
SEM images of the single-metal RPF-4 samples.
Figure 4
Figure 4
SEM images of crystals corresponding to LaYb–RPF-4 combinations; (a) La–Yb 1:9; (b) La–Yb 1:1; and (c) La–Yb 9:1.
Figure 5
Figure 5
Comparation between the input and the output metal ratio (EDS values found in the samples) of all the combinations that were synthesized in 1 day; the hollow hexagons indicate the composition of the bulk according to TXRF results.
Figure 6
Figure 6
SEM images of crystals corresponding to equimolar RPF-4 combinations.
Figure 7
Figure 7
SEM images of the crystals obtained by combining single-metal La-RPF-4 and Yb(NO3)3 (a,b) or Yb-RPF-4 and La(NO3)3 (c,d).
Figure 8
Figure 8
Relative values of formation energy for (a) various single-metal RPF-4 structures, referenced to La-RPF-4, and for (b) binary La–Yb samples. Here, the calculations were computed by starting from the corresponding single-metal structures and by replacing an increasing number of metal atom sites.
Figure 9
Figure 9
SEM images of (a) equimolar LaYb-RPF-4 synthesized in acetone/water and (b) equimolar LaGd-RPF-4 synthesized in acetone/water.
Figure 10
Figure 10
SEM images of the Yb–Er 1:1 (3 day) combination.
Figure 11
Figure 11
(a) Magnetic Field dependence of the magnetization at 1.8 K for different compounds in the series; (b) temperature dependence of the magnetic susceptibility at different measuring magnetic fields in the range of 0.1 to 5 T for Gd-RPF-4; (c) temperature dependence of the AC magnetic susceptibility at a fixed frequency of 10 KHz and amplitude of 1 Oe for different external magnetic fields for Gd-RPF-4; (d) temperature dependence, in the log scale, of the magnetic component of the specific heat for different members of the RPF-4 family.
Figure 12
Figure 12
(a) Temperature dependence of the magnetic specific heat of the Yb/Gd-RPF-4 sample under different magnetic fields and (b) magnetic field dependence of the magnetic component of the specific heat at different temperatures (isothermal).
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